1. Field of the Invention
This invention relates to a buckle device for use in a seat belt apparatus.
2. Description of Related Art
Ordinarily, this kind of buckle device has a structure in which a lock plate is moved by an urging force of a lock spring to be brought into engagement with a tongue plate or, in a state of engagement with the tongue plate, it is moved against the urging force of the lock spring by the operation of a release button to be disengaged from the tongue plate.
In buckle devices of this type, a portion of the release button is exposed outside the buckle cover for enabling the operation. There is therefore a risk of a portion of the body of the occupant or a certain object striking against the release button and accidentally moving the same and, hence, a risk of the lock plate from moving against the urging force of the lock spring by this movement of the release button, this movement, resulting in disengagement from the tongue plate. With a view to solving this problem, a type of buckle device (such as those disclosed in Japanese Utility Model Publication Nos. 62-28888 and 62-28889) has been proposed which has a stopper separately provided to restrict the movement of the release button. After the tongue plate has been engaged, the stopper is moved to prevent the release button from moving to the tongue plate releasing position.
In this type of buckle device, however, there is also a risk of the lock plate moving against the urging force of the lock spring and disengaging from the tongue plate if a large force to move the lock plate is caused by a large acceleration applied to the lock plate in the tongue plate releasing direction. In consideration of this risk, it is necessary to set a large urging force for the lock spring.